On flathub/us.zoom.Zoom#35 the checker correctly submitted an update to a newer version of Zoom. The rotating URL was then rolled back to the older version, and the checker dutifully opened flathub/us.zoom.Zoom#36. However, the latter PR prepended the new version to the appdata <releases>:

   <releases>
+    <release version="3.0.287250.0828" date="2019-08-29"/>
     <release version="3.0.291715.0908" date="2019-09-09"/>
     <release version="3.0.287250.0828" date="2019-08-29"/>

This is invalid:

Processing application us.zoom.Zoom
us.zoom.Zoom.desktop:              AppData problem: tag-invalid : <release> version was duplicated
us.zoom.Zoom.desktop:              AppData problem: tag-invalid : <release> versions are not in order [3.0.287250.0828 before 3.0.291715.0908]

Two changes suggest themselves:

• Validate the generated appdata with appstream-util before sending the PR
• Avoid generating this invalid change in the first place

The second could be done in a couple of ways:

• The cheat's way to do it is to only include one <release> in <releases> and just update it every time the version changes. However, the Zoom appdata has been dutifully preserving the full release history since before this checker entered the scene.
• The better approach would be to drop all <release> tags that do not compare older than the one we are about to prepend.